Abstract This application will test the hypothesis that inhibition of sphingosine-1 phosphate (S1P) production and signaling in lung endothelial cells by chronic cigarette smoke (CS) exposure is a critical event in emphysema pathogenesis. We propose that inhibition of sphingolipid metabolism upstream of S1P production will have a dual effect: loss of protective, pro-survival S1P production and signaling, coupled with accumulation of cytotoxic sphingolipid metabolites such as ceramide that cause cell death. We will test this paradigm primarily in lung endothelial cells, since their loss is known to be a key element of emphysema pathogenesis. Despite an abundance of data highlighting the beneficial effects of S1P on the vasculature, little is known about its regulation and importance in CS-induced lung injury and emphysema and the mechanisms by which S1P prevents or disengages various types of cell injury triggered by upstream sphingolipid metabolites. These newly uncovered cell stress responses, injury, and death are present in emphysema lungs and include mitochondria damage, inappropriate clearance by mitophagy, and a new form of cell death, necroptosis. We hypothesize that CS decreases S1P production and its S1P receptor 1-dependent signaling, leading to accumulation of necroptosis-inducing palmitoyl-ceramide and to decreased pro-survival signaling in lung endothelial cells, culminating in emphysema. We will test this hypothesis using a translational approach of CS exposure in mice coupled with primary human lung cells. Our work will provide a mechanistic link between CS, the steady and conditional state levels of S1P and cellular injury and will reveal novel therapeutic targets to limit lung destruction in this common disease.